Issue
Assistance is required to create a Sigma program that controls five chillers in a fixed sequence. The existing attempt does not function as intended.
Product Line
Satchwell BAS & SigmaEnvironment
Satchwell BAS & Sigma
Cause
- Control five chillers in a fixed sequence
- Introduce a configurable delay (default: 20 minutes) between starting each chiller
- Allow for an adjustable temperature differential to determine when chillers are activated
Resolution
The following program logic can be used:
Program Logic
10 XFlo = POINT 0|144 - POINT 0|140
20 IF XFlo <= 0.000000 THEN XFlo = 0.000000
30 IF XFlo >= POINT 0|141 THEN XFlo = POINT 0|141
40 XFlo = (XFlo / POINT 0|141) * 100.000
50 XInt = 0
60 IF XFlo >= 20.0000 THEN XInt = XInt + 1
70 IF XFlo >= 40.0000 AND YInt >= 1 THEN XInt = XInt + 1
80 IF XFlo >= 60.0000 AND YInt >= 2 THEN XInt = XInt + 1
90 IF XFlo >= 80.0000 AND YInt >= 3 THEN XInt = XInt + 1
100 IF XFlo >= 100.000 AND YInt >= 4 THEN XInt = XInt + 1
110 IF TIME LEFT THEN GOTO 180
120 IF XInt > YInt THEN GOTO 150
130 YInt = XInt
140 GOTO 190
150 ZInt = INT(POINT 0|142) * 60.0000
160 SET TIMER ZInt
170 YInt = YInt + 1
180 IF XInt < YInt THEN SET TIMER 0
190 RETURN VIA TEXT 92 VALUE FLOAT(YInt)
Object Descriptions
| Object | Type | Description |
| 140 | SPA Object | Setpoint (reference temperature) |
| 141 | SPA Object | Differential (range over which chillers activate) |
| 142 | SPA Object | Delay time (in minutes) |
| 144 | AI Object | Chiller return temperature |
Chiller Command Configuration
Each chiller command object must use hysteresis control. Configure as follows:
| Chiller | Low Setting | High Setting |
| 1 | 0.1 | 0.9 |
| 2 | 1.1 | 1.9 |
| 3 | 2.1 | 2.9 |
| 4 | 3.1 | 3.9 |
| 5 | 4.1 | 4.9 |
Additional Notes
- Ensure the programmable object is linked to the chiller command objects.
- The hysteresis settings prevent rapid cycling and ensure stable operation.
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